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King County has issued a flood warning for the Tolt River and opened its Flood Warning Center Sunday morning in anticipation of continued widespread heavy rainfall, mostly in the mountains.

Particularly heavy amounts– between three and five inches –are expected Sunday and Monday along the west slopes of the Cascades and its many river basins, according to the National Weather Service (NWS). The county said big rains overnight brought the Tolt River to minor flood stage. The river was flowing at 3,610 cubic-feet per second at 12:45 a.m. Sunday, just above the Level II flood stage threshold.

The county warned that other rivers could flood as the rains continue and urged residents in threatened areas to be vigilant.

The county said the Flood Warning Center will remain open as long as high flows are present on King County rivers. Real-time information on river flows and other flooding information is available at kingcounty.gov/flood.

National Weather Service meteorologist Johnny Berg said the weather will remain warm and that snow levels will remain high, between 6,500 and 7,000 feet. Most of the moisture — and there’s a lot of it — will fall as rain to swell the area’s rivers.

The storm was predicted to dump up to 6.5 inches of precipitation in a few mountain areas, with an average 3 to 5 inches across most the western Cascades, according to the NWS.

“There will be some snow melting, but mostly the flooding will be caused by rain that’s going to run off into the rivers,” Berg said.

Unlike most “atmospheric rivers” responsible for the region’s heaviest rainfalls, this system came from a different direction: out of the northwest, rather than from the southwest.

Part of the reason it’s going to be so wet is because the system is also very warm, Burg explained. High temperatures will reach the mid-50s over the next couple of days, with overnight lows as high as 49 degrees.

The heavy rains come on the heels of a new report by Seattle Public Utilities officials outlining their evidence that the city known for its misty drizzle is experiencing more “extreme rains,” which they believe is a preview to climate change.